I've heard people say that SACD ought to fail in transient reproduction, (because it can only encode a rise and fall relative to the last time step) so I did some calculations:

'Sampling rate' of SACD = 2.8MHz = 64x 44.1kHz

For encoding tones up to 44.1kHz at full scale, it has to reach full-scale from 0 in 64 steps, that is, at any given time there can only be 64 possible positions for the waveform.

This gives it 6 bits resolution to CD's 16 bits??

OK, suppose you only need to encode up to 22.05kHz at full scale, the number of possible positions increases from 64 to 128--7 bits resolution, big improvement

I doubt this is how DSD actually works, but this article http://www.iar-80.com/page40.html (I linked to page 40, but it seems page 1-39 may be going on and on about the sonic flaws of DSD as well) seems to take this view seriously and goes on to talk about how you try to recover musical information from the 6 bit stream.

delta: you integrate (sum) the outputsigma-delta: you integrate (sum) the input

The (not too obvious) result is that, while delta modulation can suffer from slope overload (which is what you're describing - the 22kHz sine wave is moving far too quickly for the digital staircase to track it), sigma-delta modulation does not. However, the higher frequencies are full of noise.

Think of it this way: in a basic delta modulator, if you draw a graph of frequency against allowed amplitude, then you are allowed high amplitudes at low frequencies, but only lower amplitudes and higher frequencies (otherwise you push it into slope overload).

However, in a sigma-delta system, it's as if the signal is "equialised" on the input to reduce the higher frequencies (to prevent slope overload), and then re-equalised on the output, to bring the higher frequencies back to their correct level. The result is that the higher frequency ranges contain much more noise - the modulator has an intrinsic noise, and it's amplified at higher frequencies on the output.

This is a very badly remembered way of thinking about it, and it's not quite how it works in reality. But I hope it helps!

So, basically, SACD has about 20 bits of equivalent resolution in the audio band, but terrible amounts of high frequency noise. It also has excellent time resolution. It sounds very good - whether all that high frequency noise is a good idea is a different matter entirely!

Cheers,David.

Some of the technical flaws of SA-CD:

* If you want to do some digital post processing, you must convert it to PCM. If PDM has any advantage, this advantage is removed.

* PDM is also not suitable to directly drive digital power amplifiers. It switches too often so you have to much switching losses. So PDM must converted to PCM and then to PWM.

* PDM is may be suitable to built low cost head phone DA/C+Amplifiers.

* PDM is very sensitive to asymmetries between switch on and switch off.

* Best possible converters (noise + linearity at low levels) do NOT use PDM, but - PWM - 4...16 PDM convertes in parallelBoth can not be generated by PDM, but by a PCM.

*The frequency response of the output filter of a SA-CD is not defined

- So it is not possible to compensate the effect of the output filter in the recording- It is very likely that manufacturs built gadgets with extremely wide frquency response and huge amounts of HF noise to boast with a extremely wide frequency response.

Depending on the high frequency amount the frequency overall-frequency responsecan be linearized up to 60 kHz (Pop) or 80 kHz (Classic).

-------------------------------------------------------------Another point:I have serious doubts about the need of a higher time resolution.- Modern perceptial encoder has lime resoution between 1.5 and 5 ms.- Very critical signal needs time resolution of 2...0.5 ms for f=10 kHz.- CD has something in the range of 0.2...0.3 ms for f=20 kHz and 0.04 ms for f=10 kHz.- DVD-A (96 kHz) has something in the range around 0.015...0.02 ms for f=20 kHz and0.01...0.015 ms for f=10 kHz.